Many digital data display systems require an interactive device for the operator to communicate with the associated computer system. In the prior art, many types of devices have been used. For example, inputs to the computer have been provided by keyboards, light-pens, track-balls, joy-sticks, etc. Numerous other devices and techniques have also been developed that permit direct touch identification of data on the CRT screen or other display surface. For example, in U.S. Pat. No. 4,001,807, a system is described wherein switch buttons adjacent to the CRT screen are used to identify data on the screen. Also, there are prior art approaches wherein CRT screen overlays are provided that are sensitive to touch or approaches wherein fields of sonic waves or light beams are interrupted by a finger or stylus.
The touch data entry method is very desirable because it is fast, easy, natural, flexible, inexpensive, and readily programmable. In general, touch data entry provides advantages in human factors over the other described entry methods. However, previous systems having touch data entry switches adjacent to the CRT screen had parallax errors and it was not always easy to correlate a data entry item of interest with a particular switch. Further, in some systems, it was necessary to separately push two switches; one switch designated the data column and the other switch designated the data row. Another alternative to pushing two switches was to press one switch successively. Furthermore, when the data item of interest was designated by touch data entry, the operator had to take further operator action to display designated detailed data. Data entry systems using overlays, sonic waves, and light beams have commonly been troubled with fingerprints on the overlay thus interfering with the viewing of the CRT display. Also, because of the curvature of the CRT, troubles have been encountered with reliability, repeatability of operation and inadvertent interference.